TYPO3 Core

Double mounted pages do not see other (once and double) mounted pages on the same PID.

The tree:

index

+ services
+ + exchange
+ + leasing
+ + credit
+ + delivery
+ + trade in
+ + order

+ corporate (mount to /SYSFOLDER/corporate with subst)

+ private (mount to /SYSFOLDER/private with subst)

+ SYSFOLDER
+ + corporate
+ + + trade in (mount to /services/trade in with subst)
+ + + leasing (mount to /services/leasing with subst)
+ + + delivery (mount to /services/delivery with subst)
+ + private
+ + + exchange (mount to /services/exchange with subst)
+ + + order (mount to /services/order with subst)
+ + + reports
+ + + credit (mount to /services/credit with subst)

/corporate/
/corporate/trade in/
/corporate/delivery/
The sitemap menu on these pages are fine. All links work OK.

/corporate/leasing/
Link to /private/exchange/ - OK
Link to /private/credit/ - OK
Link to /private/order/ - OK
Link to /corporate/leasing/ - OK
Link to /corporate/delivery/ - BROKEN
Link to /corporate/trade in/ - BROKEN

/corporate/delivery/
Link to /private/exchange/ - OK
Link to /private/credit/ - OK
Link to /private/order/ - OK
Link to /corporate/leasing/ - BROKEN
Link to /corporate/delivery/ - OK
Link to /corporate/trade in/ - BROKEN

/private/exchange/
Link to /private/exchange/ - OK
Link to /private/credit/ - BROKEN
Link to /private/order/ - BROKEN
Link to /corporate/leasing/ - OK
Link to /corporate/delivery/ - OK
Link to /corporate/trade in/ - OK

/private/credit/
Link to /private/exchange/ - BROKEN
Link to /private/credit/ - OK
Link to /private/order/ - BROKEN
Link to /corporate/leasing/ - OK
Link to /corporate/delivery/ - OK
Link to /corporate/trade in/ - OK

BROKEN means Typo3 shows message: The requested page didn't have a proper connection to the tree-root! MP value remain!

And URLs have lack of a part of MP var.
Expected = index.php?id=18&MP=89-174;18-103
Printed = index.php?id=18&MP=89-174
(issue imported from #M9142)