Unexpected behavior of as_datetime for dates without seconds

[jobonaf]

Description

Problem
When using as_datetime() in lubridate, I noticed that for dates without specified seconds, the returned result is incorrect and does not match the expected timestamp.

Expected Behavior
I expect as_datetime() to maintain the specified date and time regardless of whether seconds are provided. The date 2009-05-10 23:59 should result in "2009-05-10 23:59:00 UTC".

Actual Behavior
When as_datetime() is applied to "2009-05-10 23:59", the result is 2020-09-05 10:23:59 UTC, which is entirely shifted. This behavior does not occur if seconds are included:

# Problematic case (no seconds)
lubridate::as_datetime("2009-05-10 23:59")
#> [1] "2020-09-05 10:23:59 UTC"  # Unexpected output

# No issue (seconds provided)
lubridate::as_datetime("2009-05-10 23:59:45")
#> [1] "2009-05-10 23:59:45 UTC"  # Expected output

Impact

This behavior can lead to significant errors when processing datetime data without seconds. It appears that the function might be misinterpreting input.

Context

Working environment:

• R version: 3.5.2 (2018-12-20)
• Platform: x86_64-pc-linux-gnu (64-bit), running on CentOS Linux 7 (Core)
• Locale: LC_CTYPE=en_US.UTF-8, LC_TIME=en_US.UTF-8, LC_COLLATE=en_US.UTF-8, etc.
• lubridate version: 1.9.3