Possible bug with Glow Ink Sac using on normal Sign

[Ryuushen]

It drops the frames dramatically with many normal sign using glow ink sac, picture for example

Without gloow ink sac 80 frames

With glow ink sac

Same thing even without shaders

[Motschen]

This also happens in vanilla. PictureSign does not render signs differently when they're glowing.
If this is really more intense when using PictureSign, please lmk.