  We have measured and compared the characteristics of ALD-coated Planacon
MCP-PMTs (XP85112/A1-Q-L) with their non-ALD counterparts (XP85012/A1-Q). While
the later show excellent performance, the ALD-coated sensors have surprisingly
low current saturation levels (~two orders of magnitude lower than expected)
and extremely high gain recovery time (more than 7 orders of magnitude higher
than expected). We suspect that these problems might be caused by the
unexpected side-effects of the ALD process. To make a definite conclusion, more
samples need to be tested, preferably from different production runs. If our
observation were confirmed, it would mean a serious technological setback for
ALD-coated MCP-PMTs.
