I’ve now installed a sil-padauk font on Debian and am no longer just seeing boxes with hex. The name in your first example has definitely been broken, but the damage was done in http://www.openstreetmap.org/changeset/40211422 not in the changeset you referenced. It is still the same person that did it. Really it is that changeset which should receive the changeset comments.
The name on http://www.openstreetmap.org/way/245437694 has been changed from “မြို့ရှောင်လမ်း” to “ၿမိဳ႕ေရွာင္လမ္း”.
Even just on the basis of a basic understanding of how Indic scripts work, that is clearly wrong, as it is rendering with an isolated vowel sign (U+1033 MYANMAR VOWEL SIGN MON II) “ဳ” (I see a dotted circle, but that isn’t a base character, but rather a place holder for a missing one. For those not familiar with such scripts, there are generally two types of vowel marker, an isolated form, and a diacritical form. Most characters have an implied vowel, and the diacritical overrides this. It looks almost as though two conflicting vowel marks have been applied in this case, and the Debian renderer, at least, is applying the the first, but resorting to the place holder type fall-back for the second.
What they have coded here is, base character ma (presumably m, with an implied a vowel, then modified the the vowel to i, which is OK, and further modified it to “mon ii” (presumably a variant of a long vowel), which makes no sense at all.
There is a similar defect and place holder later in the name.
The renderer on Mapnik seems to have suppressed this particular vowel mark, but there is an obvious change in the name, as compared with the original, as can be seen on this tile: http://b.tile.openstreetmap.org/19/404324/237779.png Unless the original name was completely wrong, it should be obvious, even to the person who made the change, that they have made an incorrect change.
In terms of the hacked Microsoft font, this is really about the wrong font encoding, rather than the wrong font, but there is probably only one font with this broken encoding. It looks like someone has been mapping for the font!
Rather than private mail, I would suggest adding changeset comments, but make sure you get the changeset that actually made the change.