Labiovelars

Hi, again! Here is a second question. It is always stated that the
articulation of labiovelars in PIE is unknown with precision. However,
they are commonly represented orthographically as something like "kw"
for unvoiced and "gw" for voiced (as in Piotr's system). Yet, it has
always seemed to me strange that the sound literally represented by
"kw" could become the labial "p", or "gw" become "b" , as it did in
so many branches of IE (p-Celtic, Osco-Umbrian, Greek, or Germanic
in certain cases, such as Gothic "fidwor" and "wulfs"). Admittedly,
phonology is not my strong suit. However, it has has always seemed
to me that something more like "kp" or "gb" would represent better
the original pronunciation and lead more naturally to the splits
"kp"-->"kw","p" and "gb"-->"gw","b". By a little trial and error,
it does seem possible to articulate something like "kp" or "gb" in
a unitary fashion (as the early IE scripts seem to indicate speakers
felt labiovelars to be single sounds).

All of this leads me to my question: does anyone know of examples
in which the transformations "kw"-->"p" or "gw"-->"b" are actually
attested, in historical records of any language? Can it actually occur?
I know the example of Rumanian, in which words like Latin "aqua"
appear as Rumanian "apa". However, it seems that this may be a
substrate influence of the Dacian languages of the area. As far as
I know, there are no written documents tracing "aqua" --> "apa"
in Rumanian. Are there other examples? And, for those who are more
knowledgeable in phonology, is the transformation "kw"-->"p"
and "gw"-->"b" at all plausible?