The separation of glyphs can be tweaked with the the operand Tc which which when specified is added to the offset of the glyph width given the effect of characters that are further apart.

In this particular PDF the Tc= -1.44. If we follow the layout rules of the spec the glyphs will be painted more or less on top of each other.

What I think might be happening here is related to an old note in the specification. The note says that starting x of the next glyph can't be less then the previous glyph. So in the following example:

[<0027003d>90<0003>] TJ

<0003> even after the 90 shift, it can't be painted before <.. 3d>. However in the PDF in question we are apply the negative character space for each character. My best guess is that we should have similar logic for the the character spacing. If the character advance with space is less then the previous advance then we should just use the previous advance.

Any change to the core of the next layout algorithm is pretty high risk for regressions.