Exporting/ importing changes expiration date of subkeys...

[gnupgpacker]

Hello,

there occurs an issue while exporting/ importing keypair from
Windows-7/GPG-1.423 to Android-8.1/R2mail2.

Private/public key contains one main key and three subkeys, all valid til
31.12.2019:
pub xDDDC C
sub x5B9E A
sub x493D S
sub x2BE6 E

But if exporting and importing whole key, subkey x493D and subkey x2BE6
shows a (wrong) validity til 31.12.2017 only...
Key xDDDC and subkey x5B9E show correct expiration date 31.12.2019.

Additional hint: Expiration date of all (sub)keys has been extended end of
year 2017, two additional years have been added til 31.12.2019. Former
expiration date had been 31.12.2017.

*Confused* How to solve this issue?

Please refer to red marked dates!

Export GPG (Windows):
https://i.imgur.com/rgw1ZZ9.png  

Import R2mail2 (Android):
https://i.imgur.com/lAR0vgq.png

Thx + best regards,
Chris