from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QLineEdit, QTableWidget, QSplitter, QPushButton, QVBoxLayout, QFrame

app = QApplication([])


frame = QFrame()
frame.setLayout(QVBoxLayout())

splitter = QSplitter()
lineEdit = QLineEdit()
lineEdit.setAutoFillBackground(True)

# commenting out the following line fixes the lineEdit-background problem
splitter.setStyleSheet('QSplitter::handle { background-color: grey }')
splitter.setChildrenCollapsible(False)
splitter.setHandleWidth(1)

splitter.addWidget(lineEdit)

palette = lineEdit.palette()
palette.setColor(lineEdit.backgroundRole(), Qt.yellow)
lineEdit.setPalette(palette)

frame.layout().addWidget(splitter)
frame.show()

app.exec()