you mean weird as in strange the is similar  post with answers here in forum already but in short

make sure not to check on the rasterised option also check your  resolution setting  the dpi might be too low for the scale  factor of the drawing..

The following articles may help

Fonts display inconsistently when zoom after printing to PDF

When creating a pdf with pdf.pltcfg the fonts in the pdf look pixilated and not rendered correctly when zooming into the pdf.

If still experiencing issues please advise on Product / version along with the driver being used. If your able to post a sample that too will help others to comment further.

carl the first  link  tells  user to disable  lineweights  that fixes one  problem and creates another problem with line elements have no weight.

If its just for viewing a pdf with a  pfd viewer and not microstation, then I suggest training users  how to toggle on / off line weight in the pdf viewer like adobe acrobat Control 5 toggle line weights... but for improved microstion print  output yes change pdf,pltcfg file settings to high precision but also change the dpi resolution to a higher value and  make sure rasterise tick box in print dialog  is not ticked.. also make the advanced setting text searchable  this stops the text becoming part of the image and keeps it text plus the added benefit of text searchable.. all this comes at a price, file sizes get larger..but today nobody uses floppies so file isnt  real big  priority, reabability is far more important... just as we dont  use paper much nowdays its  all pdfs and cloud based transfer not so much email dependance today.

Zooming in with a viewer has many  issues , resolution, scale, zooming in is a magnifying of the details  includes lines and text look thicker etc  for example if you draw a  map of  Australia and want to print  it  to A0 and still be able to read all the lines for  highways and read the city names and  major highways its going to be something  like 1;250 000 .. we draw  1:1 and print to paper scale down to printer by paper size...my min finished paper size  prints min text is 1.8 mm  so thats a  lot for the  program to squeeze down to 1:250, 000  so my  resolutions needs to be more that 600 dpi  at least double that to take advantage of zoomed in detail viewability.  some times we  forget that on a drawing were interested in the big picture but because we have  detail available  people  who look at the plan want to look at the nuts and  bolts when its just a general arrangement and  need to have a detail plan set for details... can still uses same xrefs  just the scale of the sheet changes and doesnt show everything...just the detail needed...  I was doing  lots of road construction work and in order to read all the call out notes I had to make  hi res and also teach everyone to use the weight on off toggle in acrobat when things were zoomed in to see drainage pit type or bollards from the survey xrefs... necessary detail but not needed in the overall picture. 

Good day! Very interesting.